This invention relates generally to a particle beam generator, and in particular to an apparatus which uses a radioactive source to generate a continuous focused monoenergetic electron beam.
Some measurements, calibrations, and physics experiments require an electron beam with high energy and narrow width, as well as sufficient flux to allow particle by particle pulse measurement. Backgrounds such as gamma rays and low energy electrons which could interfere with time coincidences on electrons must be eliminated.
Particle accelerators of the prior art which rely on electrical acceleration and electromagnetic focusing require expensive power supplies and maintenance, including adjustment and regulation of several power supplies during operation.
Collimators of the prior art when used in conjunction with radioactive sources typically produce a narrowed beam by channeling particles emitted in a forward direction. Because particles are selected from a relatively narrow solid angle significant numbers of particles at the energy of interest are eliminated. The resultant collimated beam is generally unfocused and is comprised of particles at all energy levels emitted by the source. In addition, gamma rays are not attenuated in the forward direction.
Principals of momentum selection through dispersion are known to the prior art (see Steffen, Klaus G., "Composite Systems & Spectrometers-Nondispersive Deflecting Systems", High Energy Beam Optics, 1965, pp. 113-117) and have been applied to accelerator generated particle beams (see U.S. Pat. No. 4,726,046, Nunan).
However, no single instrument of the prior art uses a radioactive source and efficiently combines functions of momentum selection through dispersion with means for demagnification to produce a focused monoenergetic particle beam.
It is therefore primary object of this invention to provide an apparatus for generation of a particle beam with high energy and flux, which eliminates or greatly reduces the amount of electrical power required and is inexpensive to construct and to operate when compared to particle beam accelerators of the prior art.
In the accomplishment of the foregoing object, it is another important object of this invention to provide an apparatus which uses a radioactive source to generate a monoenergetic electron beam of high energy and flux, while attenuating gamma rays and low energy electrons.
It is another important object of this invention to provide an apparatus which demagnifies an electron beam derived from a radioactive source, and focuses the electron beam to a spot with at least one narrow cross-dimension.
It is a further object of this invention to present an apparatus which requires no adjustment during operation.
A yet further object of the present invention is to present an apparatus which selects from particles emitted from a radioactive source those having momentum within a desired range and focuses the resultant beam to a narrow spot.
It is also an object of the present invention to provide a beam transport apparatus which eliminates bulky and expensive electromagnets and incorporates inexpensive and easily worked ceramic magnet material into permanent dipole and quadrupole magnet systems.
Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.